1. Field of the Invention
The present invention relates generally to magnetic recording/playback devices and more particularly, to an improved magnetic read/write head-positioning apparatus including means for damping lead screw oscillations.
2. Description of the Prior Art
In magnetic recording/playback apparatus used with flexible or floppy disk recording mediums, a positioning mechanism is employed to move a magnetic head radially across concentric recording tracks on the disk surface while maintaining the head in contact with the disk surface. Typically, the head-positioning mechanism includes a stepping motor for driving a lead screw rotatably mounted to its shaft, a guide rod, and a carriage mounted to the lead screw and movable thereby along the guide rod. The carriage includes the read/write head and a load arm for maintaining the disk in compliance with the transducing surface of the magnetic head. Heretofore, the lead screw has been mounted to the stepping motor with its distal end either cantilevered as illustrated in the U.S. Pat. No. 3,226,700, to Miller, or supported by a bracket which is journaled thereto as shown in the U.S. Pat. No. 3,731,292, to Kelley. Energization of the stepping motor rotates the lead screw to drive the carriage across the disk in such a manner as to enable the magnetic head to radially access a selected one of the tracks on the disk surface.
In such apparatus employing a cantilevered lead screw, vibration problems have been encountered as the magnetic head is accessed from one track to another. More particularly, the interaction between the lead screw and the carriage as the lead screw is actuated by the stepping motor causes transverse forces to be exerted on the lead screw, and the stepping frequency (the seek rate) is such as to cause the forces to excite the lead screw at its natural or resonant frequency, the lead screw will vibrate in a more or less sinusoidal manner and induce a consequent displacement of the magnetic head relative to the disk. This, of course, causes the signal output developed by the head to vary and distort the signal being recorded or played back. In instances of severe vibrations, the magnetic head may even be unloaded from the disk, causing the read signal to be lost entirely.